Electromechanical Coupling in Potentiation of Muscular Contraction

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Abstract
Diverse potentiators of contraction have basically identical, activestate mechanical effects, but act by different membrane-mediated electromechanical coupling mechanisms. The falling phase of the action potential is greatly prolonged by Zn2+ (0.1 mM) and UO22+ (0.5 to 1 µM), neither of which affects the mechanical threshold. Caffeine (1 mM), like the lyotropic anions, acts conversely. Thus changes in the duration and mechanical threshold of the action potential determine independent electromechanical coupling processes which can act individually, or conjointly in the action of other potentiators, in determining the duration of the active state and thus the potentiation of twitch tension.